ExprLib dualtime: a few small fixes, added two-equation ODE test, some cleanup, and Matlab files for testing tests
- added ExpDecay2CoupledRHS expression and related dualtimeOscillationTest
- renamed dualtimeTest to dualTimeExpDecayTest (renamed executable to dualtime_exp_test)
- fixed dualtimeExpDecayTest to compare STATE_N against the solution at t=tend, because STATE_NP1 is overwritten at the end of a step
- added Matlab files for verification of dualtime_exp_test and dualtime_oscillation_test
- fixed iteration count to start at zero instead of one
- added line to send dual time convergence history (iter count, norm) to stdout for debugging - currently commented-out